GMAT Challenge Question: Sentence Correction Is the (Tar) Pits

Once again, it’s time for a GMAT challenge question! This installment features the dreaded maximum-word-count, everything-underlined Sentence Correction device. Can you avoid getting sucked into a La Brea Tar Pit of wasted time? Here’s the question, courtesy of Boston GMAT tutor Ashley Newman-Owens; check back later for the solution and some tips for working through a problem like this:

Based on accelerator mass spectrometry, an advanced technique that makes it possible to obtain radiocarbon dates from samples much smaller than that necessary for traditional radiocarbon dating, scholars have been able to determine impressively precise radiocarbon ages for samples of Glyptodon and Holmesina recovered from the La Brea Tar Pits, extinct large mammals similar to armadillos.

(A) Based on accelerator mass spectrometry, an advanced technique that makes it possible to obtain radiocarbon dates from samples much smaller than that necessary for traditional radiocarbon dating, scholars have been able to determine impressively precise radiocarbon ages for samples of Glyptodon and Holmesina recovered from the La Brea Tar Pits, extinct large mammals similar to armadillos.

(B) Based on accelerator mass spectrometry, an advanced technique that makes it possible to obtain radiocarbon dates from samples much smaller than necessary for traditional radiocarbon dating, scholars have been able to determine impressively precise radiocarbon ages for samples of Glyptodon and Holmesina, extinct large mammals similar to armadillos, recovered from the La Brea Tar Pits.

(C) Using accelerator mass spectrometry, an advanced technique that makes it possible to obtain radiocarbon dates from samples much smaller than those necessary for traditional radiocarbon dating, scholars have been able to determine impressively precise radiocarbon ages for samples of Glyptodon and Holmesina, extinct large mammals similar to armadillos, recovered from the La Brea Tar Pits.

(D) Basing them on accelerator mass spectrometry, which allowed them to obtain radiocarbon dates from samples much smaller than those necessary for traditional radiocarbon dating, scholars have been able to determine impressively precise radiocarbon ages for samples of Glyptodon and Holmesina, extinct large mammals similar to armadillos, recovered from the La Brea Tar Pits.

(E) The use of accelerator mass spectrometry, an advanced technique that makes it possible to obtain radiocarbon dates from samples much smaller than those necessary for traditional radiocarbon dating, have enabled scholars to determine impressively precise radiocarbon ages for samples of Glyptodon and Holmesina recovered from the La Brea Tar Pits, extinct large mammals similar to armadillos.

UPDATE: Solution.

Since this sentence is underlined in its (incredibly long) entirety, you can save yourself an especially hefty chunk of time by looking for differences that jump out between the answer choices. Scanning only the ends of the answers choices reveals a split between two possible endings; the choice in the original sentence improperly situates extinct large mammals similar to armadillos, an appositive which should immediately follow Glyptodon and Holmesina. The introductory phrase is a modifier that attempts to link to scholars. The participle using makes this link legitimate, because it describes the scholars’ activity.

(A) Based on … incorrectly modifies scholars; the comparison between samples (plural) and that (singular) is awkward; extinct large mammals is not in proper apposition to Glyptodon and Holmesina.

(B) Based on … incorrectly modifies scholars; the sentence lacks a noun after than to stand in comparison to samples.

(C) Correct. Using accelerator mass spectrometry correctly modifies scholars; samples and those stand properly in comparison; extinct large mammals … is in appropriate apposition to Glyptodon and Holmesina.

(D) In both of its appearances, the pronoun them lacks a clear reference.

(E) Verb agreement problem. The singular subject, use, does not agree with the plural verb have enabled.

5 Responses

1. Eliminate E because have here points not to scholars but to the technique.
2. Eliminate A because Tar pits are not extinct animals.
3. Eliminate B also because Based on ….. scholars ( not so good when we have Using …scholar in option C).
4. Eliminate D since them used twice has no clarity on its pronoun reference.

A – Samples – that (plural – singular). Also tries to say that pits are extinct large animals
B – Compares samples to necessary (illogical comparison). Corrects the mistake that was made in A though
C – Corrects both the mistakes that were in A and B
D – Spectrometry should be followed by an apositive. Corrects the mistake that was made in A though
E – The use of …… have. should be has instead of have. (subject verb agreement)

The ‘scholars” are not “based on”, rather “scholars” are “using the accelerator mass spectrometry [to…]”. The “Using…” modifies the scholars.

“Samples” are not “much smaller than THAT…”, rather “samples” are “much smaller than THOSE…”. This is a parallelism issue – when comparing or contrasting, the items of interest should both be in the right form: plural or singular.

The placement of “extinct large mammals similar to armadillos” is acting as an appositive for “La Brea Tar Pits” when the phrase (“extinct large….”), given the context, is intended to be an appositive for “Glyptodon and Holmesina”. So, placing this phrase next to “Glyptodon and Holmesina” is correct.

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